Among aliphatic polyesters considered to give little load to the natural environment due to their biodegradability or hydrolyzability, polyglycolic acid resin has a particularly extensive decomposability, is excellent in mechanical strengths such as tensile strength and in gas-barrier property when formed into a film or sheet, and is therefore expected to be used as fishery materials, such as fishing yarns, fishery nets and culturing nets, agricultural material, or various packaging (container) materials (e.g., Patent documents 1-3 listed below). However, the severe hydrolyzability of polyglycolic acid resin has frequently provided a factor of obstructing the application thereof. For example, in the case of obtaining various forms, such as filament, film and sheet, an ordinary thermoplastic resin is generally melted, cooled, solidified and pelletized to obtain a particulate forming resin material, which is then supplied for various forming processes. However, regarding the cooling step among the above-mentioned series of steps, cooling with water has been believed impossible or impractical for polyglycolic acid resin having severe hydrolyzability. This is because polyglycolic acid resin is hydrolyzed in a stage when a melt thereof is introduced into water to be cooled, thus resulting in a polyglycolic acid resin having a lower molecular weight which slows a non-ignorable degree of lowering in moisture resistance (i.e., a further lowering in molecular weight due to further hydrolysis under the condition of use thereof and an accompanying lowering in practical strength). Incidentally, Patent document 4 listed below discloses a method of crystallization of aliphatic polyesters including a polyglycolic acid resin, comprising: causing an aliphatic polyester in a solid state, a molten state or a solution state to contact a liquid including water to solidify and crystallize the aliphatic polyester, but no working example is disclosed regarding polyglycolic acid resin. For the above-mentioned reason, the cooling subsequent to melting for formation of particulate forming material of polyglycolic acid resin has been effected by air cooling (i.e., cooling by contact with air). According to the present inventors' experience, however, when a melt-extrudate (strand) of polyglycolic acid resin is solidified by air cooling, for example, the strands after solidification are distorted and, when pelletized (e.g., into cylindrical pellets) by means of a cutter, etc., provide a particulate product having a broad particle size distribution, which is inconvenient for a subsequent product forming step. Further, when the number of strands is increased in order to increase the productivity, inconveniences, such as entanglement and adhesion of the strands, are liable to occur.    Patent document 1: WO2003/037956A1    Patent document 2: JP10-60136A    Patent document 3: WO2005/072944A1    Patent document 4: JP2000-302855A